A scramjet (supersonic combustion ramjet) is a variation of a ramjet with the distinction being that the combustion process takes place supersonically. A scramjet engine includes a constricted path, through which inlet air is compressed by the high speed of the vehicle; a combustion chamber where fuel is combusted; and an expanding exhaust portion through which the exhaust jet leaves at higher speed than the inlet air.
Although scramjets are an example of an asset having a supersonic fluid inlet, there are many others. When supersonic inlets are brought up to operational speed from lower speeds, a build-up of air can create a standoff shock in front of the inlet, preventing the air from streaming through the inlet, into the engine, without first going through this undesired and non-optimal shockwave. Such a shockwave can prevent, for example, a scramjet engine from properly operating; therefore, it is desired for such shockwaves to be minimized, lessened, or eliminated. Once the air is flowing properly through the necked down region of the inlet, the supersonic flow through the inlet can take place as designed, and the inlet is said to be “started”.
There are several ways that have been considered to date to address the presence of an undesired shockwave at an inlet. One approach at a scramjet inlet, for example, is to “swallow the shock”. This can be done by increasing the speed of the air vehicle to force the stand-off shock, and the air backed up behind it, to squeeze through the smallest point (i.e., throat or neck) of the inlet. This requires that the engine(s) be oversized by 20-25%, which is a large concern when designing supersonic or hypersonic air vehicles. In particular, for example, there are many design trades that need to be made, and having a powerplant that is 25% too heavy prevents designers from meeting all of the constraints on mass, lift, power, drag, etc.
One proposed way to address the undesired shockwave at the opening of an unstarted supersonic or hypersonic inlet, in particular for scramjet engine inlets, is to cover the inlet holding a roughly evacuated space behind that covering (not just covering the neck/throat of the inlet, but covering the whole open region) until the vehicle gets up to the operational design speed, and then removing/rupturing the covering membrane, at which point the inlet starts because there is no built up air blocking the flow. This approach is, at best, feasible as a one-time solution; however, if the inlet failed to start the first time, or if the vehicle had to slow for some reason during flight or un-start the inlet in any other way during flight and then come up to speed and re-start the engine, it would be impractical to cover the inlet again while in flight to evacuate the region behind it.
Another approach, considered to address the problem related to scramjet engine inlet starts/restarts, is to employ fixed geometry systems that typically rely on passive means to start the inlet system, using bleed holes or slots to reduce the mass capture to an amount required to allow sonic flow at the throat. The problem is that these system lead to large inefficiency in that once the inlet is started, these same holes result in increased inlet drag and typically allow a small amount of capture mass to escape without being ingested into the engine. FIG. 1, for example, illustrates a conventional streamtraced Busemann inlet having an inlet neck that narrows to a small opening, through which all air entering the inlet has to be funneled, prior to entering the combustion portion of the engine. The geometry of the Busemann inlet is modified, in some circumstances, by slitting the inlet open to allow some of the captured air to spill out of the inlet if it can not stream through the flow path unimpeded. This narrowing structure of the Busemann inlet is further illustrated via the spatial grid that is provided in FIG. 1, which depicts the relative circumferences of the inlet edge of the Busemann inlet and the throat region of the Busemann inlet.
Another approach to swallowing the shock is to mechanically open the throat, allow the shock to pass through, and then neck the throat down to the designed operating geometry. The required mechanical actuators, however, are relatively slow and add weight and risk of failure to the engine system.
Supersonic and hypersonic flows also have undesirable effects on the inner surfaces of wind tunnels, such as the throat region of supersonic or hypersonic wind tunnels. Wind tunnels, in this regard, are research tools developed to assist with studying the effects of air moving over or around solid objects. Current hypersonic wind tunnels fall into two basic categories: long duration (blow-down and continuous) facilities and short duration (impulse) facilities. For both categories, throat erosion within the wind tunnel, due to excessive heat transfer from hypersonic and supersonic flow, is a major performance and maintenance concern. In addition, certain facilities are often limited to fixed or single Mach number capabilities.
Other sources of shock waves, blast waves, and associated supersonic or hypersonic flow are improvised explosive devices (IEDs), bombs, landmines, or the like, which are often placed within the driving surface or on the side of roads, so as to detonate in the presence of passing vehicles. When such devices discharge near (such as under) a vehicle, the shockwave associated with such IED detonation can impart substantial damage to the vehicle/cargo and, most disturbingly, to the occupants of the vehicle.
Accordingly, there is a need within many contexts for a way to control, mitigate, and/or effect shock waves, blast waves, supersonic flows, and/or hypersonic flows, in relation to assets, such as air vehicles, ground vehicles, wind tunnels, and the like.